He doesn't initiate anything, doesn't want any kind of physical contact with you other than the mechanicals and does nothing for your pleasure.
OK, that's bed.
What about the rest of your relationship?
Do you get on well otherwise, talk, laugh, share, travel, go out to dinner, see shows, socialise, do hobbies etc together? All the things people do in a relationship?
If yes, then that's all good.
It's just that the sex isn't.
There could be many reasons.
It could just be a lazy habit.
He could simply not like, want or enjoy sex at all.
He may as some have suggested be a closeted gay man, as happened to a friend of my mother's after children and grandchildren.
Only you know what you've done so far to deal with it.
But if being used as a sex aid is no longer acceptable, order him a catalogue and tell him as your relationship has been sexless for a long time, he can make a collection of items he can use any time and not make you feel like a gadget.
And if sex on your terms is important to you, and he will not change, it may be time to consider.
Do you want to remain in the relationship at all?
If yes and you have a happy life in all other aspects, do you need to seek that one piece of fulfilment outside your marriage?
Then as to how - a lover? Beware emotional mess.
A professional? Probably expensive.
A club of some sort? Personal health and safety are essential.
A lot of thinking to do.